Devour Devouring Contacts!!

A friend of mine has a devour and is experiencing the following issues:
His contacts keep erasing from his phone book. All at once and it's always the next day after they were saved. I know he's not putting them in wrong because i went back and put a few in as a test.
I noticed he had 3rd party apps enabled and i unenabled it but we still have issues.
As far as apps go, i'm not sure what he has but i know he has primarily been DL'ing from the market.
I'll be asking if he's DL'd anything from a site that doesn't redirectto the market when i see him next but till then, what does this sound like it could be?

where is he entering the contacts? in to gmail or directly onto the phone? can you confirm that when the contacts are entered they are being synced up with gmail? I have not personally had this problem but it sounds like a sync problem, where the contacts are not getting backed up to gmail and then gmail is clearing the contacts from the phone. Another thing to try is to get all of the contacts setup directly through gmail and then do a full hard reset on the phone to see if the problem persists...